In fabrication of a semiconductor device, various kinds of heat treatments, such as film formation, oxidation and diffusion, modification, and annealing, are performed on a semiconductor wafer (hereinafter, simply referred to as a wafer) as a to-be-treated substrate. As a semiconductor device is required to have a high speed and to be highly integrated, annealing following ion implantation requires a higher speed of rise and fall of a temperature to minimally inhibit the diffusion. As such an annealing device capable of raising and lowering the temperature at a high speed, there is suggested an annealing device using a light emitting diode (LED) as a heating source (for example, Japanese Laid-Open Patent Publication No. 2005-536045).
However, when the LED is used as the heating source for the annealing device, it is necessary to generate a large amount of light energy in response to rapid heating. Thus, the LED has to be mounted with a high density.
An LED element is a compound semiconductor made of a compound, such as GaAs, GaN, or the like. Such a material has a very high refractive index against light, that is, approximately 2.5˜3.6, and thus reflects approximately 15% of the light with even an incident angle of 0°. Accordingly, when such a material is exposed to air, the extracted light efficiency is highly lowered. For this reason, in a case where the light from the LED element is extracted in air (vacuum), it is considered to fill any material having a refractive index between the above mentioned high-refractive index material and air, such as a transparent resin.
Meanwhile, from the standpoint of the shape, the LED element has a length of approximately 0.3˜0.5 mm on each side, and a thickness of approximately 0.2 mm. Accordingly, when the bottom surface of the LED element is attached onto a substrate, since the total area of four side surfaces is larger than the area of the top surface, it is important to efficiently extract the emitted light from the side of the LED element. However, when a disposition space of the LED element is merely filled up by a resin as described above, the light emitted from the side of LED element cannot be sufficiently extracted.